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Re: [PATCH v2 4/5] arm/mpu: Implement ioremap_attr for MPU
- To: "Orzel, Michal" <michal.orzel@xxxxxxx>
- From: Hari Limaye <Hari.Limaye@xxxxxxx>
- Date: Thu, 28 Aug 2025 09:37:12 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Luca Fancellu <Luca.Fancellu@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Thu, 28 Aug 2025 09:37:58 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-index: AQHcF/ycst5ZxM1WdEyQIzD/TwjB3bR3zqQA
- Thread-topic: [PATCH v2 4/5] arm/mpu: Implement ioremap_attr for MPU
Hi Michal,
>>
>> + rc = mpumap_contains_region(xen_mpumap, max_mpu_regions, start, end,
>> &idx);
>> + if ( rc < 0 )
>> + panic("Cannot handle overlapping MPU memory protection regions\n");
> Why panic? This function is not used only at boot time and should propagate
> error to the caller, it's also within a spin lock.
Good point - I will update this to propagate the error in the next version of
the series.
>> + /* This API is only meant to unmap transient regions */
>> + if ( !region_is_transient(&xen_mpumap[idx]) )
> So is this the only purpose of the transient flag? To check that
> unmap_mm_range
> is used on the range that was mapped with map_mm_range? What would happen
> without introducing this flag? You already check for the matching attributes.
>
> ~Michal
>
Yes this is the purpose of the transient flag - we want to ensure that a call
to unmap_mm_range only destroys a mapping that was created by a matching call
to map_mm_range. Due to the fact that map_mm_range may not create a mapping in
the instance that one already exists - `/* Already mapped with same attributes
*/` - we need this check to ensure that unmap_mm_range will not destroy a
pre-existing mapping.
Many thanks,
Hari
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